It is somewhat ironic that contemporary technology provides materials, such as carpets, which need replacement not because the fabric wears out, but because the fabric becomes stained to the point of being unsightly. Contemporary technology makes available extremely wear-resistant fabrics; contemporary technology also makes available such items as colored food drinks directed to a class of users (young children) whose nature virtually assures repeated spillage. The combination of these advances has spawned the need for making fabrics more resistant to staining; we want to create an "invisible barrier" on fabrics to various dyes.
As will be described in greater detail within, the fabrics of greatest pertinence to our invention are polyamides, and methods of increasing their stain resistance have been described. Some methods employ additives to reduce the wettability of the material. Other additives appear to coat and impregnate the fibers of the finished product, which increases their period of anti-stain effectiveness, and chief among the latter are aromatic sulfonic acids and, perhaps, sulfones. For example, a mixture of condensation products of formaldehyde with phenolsulfones, phenolsulfonic acids, and phenolsulfone sulfonic acids are used for nylon (polyamide) carpets, where relatively high molecular weight materials appear to be most efficacious when used alone (U.S. Pat. No. 4,592,940) and lower molecular weight materials are desirable only in the presence of alkali metal silicates (U.S. Pat. No. 4,501,591).
There are several disadvantages to the use of aromatic sulfonic acids as stain resistant agents. The major concern is their photoinstability which leads to their yellowing and thereby imparting a yellow cast on materials which have been treated with these sulfonic acids. Another, indirect concern is an environmental one. The process by which such sulfonic acids are made afford a plethora of products, some of which are or may be environmentally hazardous according to EPA standards. Thus there is a need for anti-staining agents which do not suffer from the above disadvantages.
The teaching of Bridgeford (U.S. Pat. No. 3,689,466) of polymeric alcohol sulfonic acids containing S-xanthogenate ester substituents as anti-staining agents appears to be singular with respect to non-aromatic sulfonic acids. A fair summary of the prior art is that anti-staining agents are most desirably aromatic sulfonic acids containing a substantial amount of sulfones and of high molecular weight unless used in conjunction with an alkali metal silicate as an additive, and that where a non-aromatic sulfonic acid is used it is as a high molecular weight polymeric material where the S-xanthogenate moiety is an integral and indispensable part of the anti-stain agent.
Our invention is the use of simple, relatively low molecular weight aliphatic sulfonic acids as agents which impart stain resistance to fabrics containing free amino groups. The aliphatic sulfonic acids which are used as stain resistant agents in this invention are environmentally safe, are biodegradable, and are prepared without environmental hazards. The aliphatic sulfonic acids of our invention are effective at relatively low levels and are effective without the presence of additives. Our stain resistant agents are non-yellowing, are inexpensive, are readily available in the marketplace, and are easy to apply.